<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    .box {
      width: 200px;
      height: 200px;
    }

    .nav {
      color: aqua;
      background-color: blue;
    }
  </style>
</head>

<body>
  <div class="box">qwqwqw</div>
  <script>
    const box = document.querySelector('.box')
    box.classList.add('nav')

    box.classList.remove('nav')

    box.classList.toggle('nav')
  </script>
</body>

</html>